Spatial attention is the process that enables us to scrutinize one region of visual space at the expense of others. Surprisingly little is known about the neural mechanisms of attention. We will use fMRI technology to investigate the effects of spatial attention in several early visual areas (V1, V2, V3, V3A, V4, VP, MT, and the LGN). First, we intend to localize and further quantify the effects of spatial attention observed in these early visual areas. We will map the retinotopic organization of attentional effects and determine whether the pattern and magnitude of activity observed in the brain correlates with the location and degree to which spatial attention is allocated. Second, we seek to localize the regions of extrastriate visual cortex that respond when attention is differentially allocated to specific object features. Third, we hope to establish a quantitative and predictable relationship between neural activity and behavioral responses during tasks that tax attentional resources. These results will shed light on the neural substrates of attention and will hopefully provide valuable information that leads to a treatment for attention-related ailments such as dyslexia and attention deficit disorder (ADD).